Multiple-disc type filters generally include a housing in which the filter body within the housing is in the form of a stack of like, centrally-apertured, filter discs having grooved side faces defining filtering channels between the adjacent discs in the stack. In some applications of such filters, the outer face of the stack of filter discs constitutes the upstream side of the filter, in which case the fluid being filtered passes from the outer face to the inner face of the stack. In other applications of such filters, the inner face of the stack constitutes the upstream side of the filter, in which case the fluid being filtered passes from the inner to the outer face through the filter stack.
Multiple-disc type filters have a number of advantages over other known types of filters, for example, the cylindrical-screen type filter. The multiple-disc filter has a larger capacity for removing and retaining dirt particles, since these may be retained also between the side faces of the discs, in addition to being retained on the upstream surface as in the cylindrical-screen type filter. Another advantage in the multiple-disc filter is that it is not as easily ruptured as the screen type and therefore there is less danger that because of a malfunction, unfiltered water may pass through and clog sprinklers or other devices downstream of the filter. The latter advantage is particularly important in self-cleaning filters wherein the upstream face of the filter is cleaned by a cleaning nozzle which, in the case of a screen-type filter, may rupture the screen by particles becoming wedged between the cleaning nozzle and the filter screen.
The stack of discs in the multiple-disc type filter has hitherto been supported internally by a cylinder pierced with holes so as to allow the fluid being filtered to flow therethrough. Since the stack is held in position by fastening members at each end, as for example by annular screws which move about threaded extensions of the cylinder at each end thereof, the spreading of the discs for cleaning can be a laborious process. If it is desired not to remove the discs from the stack for cleaning, an in-line extension of the central cylinder is required. Such extension adds to the size and cost of the equipment and is not practical for non-in line systems.